Development system employing a coronode immersed in a liquid developer

ABSTRACT

THE SUBJECT MATTER OF THIS PATENT APPLICATION IS DIRECTED TO A NOVEL PROCESS OF IMAGE DEVELOPMENT UTILIZING CONVENTIONAL LIQUID DEVELOPERS. IT HAS BEEN DETERMINED THAT DUE TO THE STRATEGIC PLACEMENT OF A CORONODE BENEATH THE SURFACE OF A LIQUID DEVELOPER THE DEVELOPMENT ZONE MAY BE LOCALIZED AND DEVELOPMENT ACTION CONTROLLED EXTERNAL-   LY BY SELECTIVELY DEFORMING THE LIQUID DEVELOPER THUS RESTRICTING CONTACT OF SAID DEVELOPER TO THE PARTICULAR IMAGE AREAS TO BE DEVELOPED.

Apr1l27, 1971 c, SNELLING 3,576,623

DEVELOPMENT SYSTEM EMPLOYING A CORONODE- IMMERSED IN A LIQUID DEVELOPER Filed Feb. 23, 1958 INVENTOR.

CHRISTOPHER SNE LING BY 19% W ATTORNEYS United States Patent 3,576,623 DEVELOPMENT SYSTEM EMPLOYI NG A CORONODE IMMERSED IN A LIQUID DEVELOPER Christopher Snelling, Penfield, N.Y., assignor to Xerox Corporation, Rochester, N.Y. Filed Feb. 23, 1968, Ser. No. 707,574 Int. Cl. G03g 13/10 US. Cl. 96-1 3 Claims ABSTRACT OF THE DISCLOSURE The subject matter of this patent application is directed to a novel process of image development utilizing conventional liquid developers. It has been determined that due to the strategic placement of a coronode beneath the surface of a liquid developer the development zone may be localized and development action controlled externally by selectively deforming the liquid developer thus restricting contact of said developer to the particular image areas to be developed.

BACKGROUND OF THE INVENTION This invention relates to an imaging system and, more specifically, to an improved development system for electrostatic latent images.

It is known that electrostatic latent images may be formed and developed on the surface of certain high resistant materials, and subsequently converted into a visible image. For example, an electrostatic pattern may be formed on an insulating substrate such as by exposure to a potential source through a stencil. In the case of a photoconductive insulating material, a uniform charge is deposited on the particular surface and then dissipated by selective exposure to a pattern of activating electromag netic radiation. Whether formed by these or some other means, the resulting charge pattern is conventionally made visible by development with electroscopic marking particles through electrostatic attraction thus forming a visible image or image body of electroscopic matter corresponding to the latent image. This image may then be fixed in place or transferred to a secondary surface to form the final print. Other forms of development have been utilized such as bringing the surface bearing the latent electrostatic image into contact with a body of liquid developer, either by immersion of the image bearing surface or by flowing the liquid developer across the surface of the image bearing member. Generally, in this method, the developer comprises a [finely divided opaque solid dispersed in a liquid having a high electrical resistance.

While the liquid development approach has certain distinct advantages over the use of dry development techniques, such as greater simplicity and increased speed of operation coupled with improved control and versatility in the development process there are inherent disadvantages in such a system. While increasing the speed of development and therefore the speed of the entire printing process, the liquid development approach still provides a process wherein there is no apparent technique whereby the amount of developer which contacts the surface of the image bearing member may be effectively controlled. Furthermore, it is generally necessary to introduce an additional mechanism into the system to provide for a uniform developer medium in the development zone.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention to provide an imaging system which will overcome the above noted disadvantages.

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It is a further object of this invention to provide a novel imaging system capable of producing high contrast images.

Another object of this invention is to provide a novel liquid development process capable of localized control at the site of image development.

Yet, another object of this invention is to provide a liquid development system 'which insures increased speed of development while simultaneously replenishing the depleted developer in the development zone.

A further object of this invention is to provide a novel liquid development imaging system which applies nonuniform electric -field phenomena in a liquid developer process.

It is a still further object of this invention to provide a novel imaging system wherein the potential source serves as both the development force as well as the means for insuring the presentation of uniform developer at the site of development.

Yet, still a further object of this invention is to provide a liquid development system which is capable of regulating image density.

The foregoing objects and others are accomplished in accordance with the present invention, generally speaking, by providing a development process whereby an electrostatic charge pattern is formed on the surface of a high resistance material. The resulting pattern is brought into close association with a liquid developer. Present beneath the surface of the liquid developer is positioned at least one coronode unit capable of emitting charge to the surrounding liquid environment. The development system consists of a point source-to-plane imaging system. By applying a voltage to the immersed coronode, deformation of the liquid developer surface can be controlled by regulating the magnitude of the voltage applied and the location of the coronode within the developer so as to selectively contact the electrostatic charge pattern onthe surface of the image bearing member. The resulting developed image may be fixed in situ or transferred to a secondary substrate. In an alternate embodiment of the present invention, the developer liquid may be presented to the surface of the image bearing member in the form of a liquid spray by electrostatic atomization continuously generated and simultaneously charged by the coronode unit immersed in the developer. Furthermore, by adapting the process of the present invention to a polychromatic imaging system, utilizing the proper filter systems it is possible to produce a multicolor print in a stepwise mode by selective displacement of a liquid developer contain ing the proper colorant in a manner 'which eliminates conventional registration problems.

It has been determined in the course of the present invention that the presence of a coronode beneath the surface of a liquid developer increases the development speed by insuring that pigment or toner depleted during the development process is quickly replaced by fresh developer. This results from the pumping action caused by the discharge of the coronode (electrode) in the liquid. The system comprises a point-to-plane electrode arrangement. The development zone may be localized and development action controlled externally by this means of deforming the liquid surface thus providing a technique of regulating image density. Furthermore, the process of the present invention also insures homogeneous particle charge polarity. The charging of the suspended pigmented or toner particles by eiher charge transfer from the ionized liquid or direct contact with the coronode allows for the use of not only those developer materials which heretonow have been found suitable in a liquid development process, but also permits the use of normally unsuitable developer material. When the expression point source is used in the course of the present invention it is intended to mean a localized source of energy such as a needle, wire, thin knife-like edge or other similar device.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further defined in the accompanying illustrations in which:

'FIG. 1 represents a continuous imaging and development process of the present invention utilizing a dielectric drum as the image support member.

FIG. 2 represents a continuous imaging and development process of the present invention utilizing a photoconductive drum as the image support member.

DETAILED DESCRIPTION Referring now to FIG. 1 there is seen a rotary drum 1 which for the sake of the present illustration will be represented as a dielectric material such as Mylar, polyethylene terephthalate, commercially available from E. I. du Pont de Nemours & Co. Represented on the surface of the highly resistant material is an electrostatic charge pattern 3 representing the image which is to be reproduced, formed at exposure station 4. Positioned beneath the drum or imaging substrate 1 is a trough like container 5 which carries a developing liquid 6 consisting of a dispersion of a color supplying component in a neutral organic liquid with high electrical resistivity and low dielectric constant. Immersed in the insulating liquid developer in .an electrode 7. herein represented as a longitudinally situated knifeedge electron source, a substantial portion of which is overcoated with a dielectric material 8. Although various electrode spacings may be employed the edge of the knife like electrode in the present case will be located from about .5 to about 5 mm. from the surface of the insulating liquid. A high voltage source 10 connects the immersed electrode 7 to ground. By controlling the potential applied by the voltage source 10, the surface of the insulating liquid developer may be deformed selectively so as to contact the surface of the image bearing drum when the latent image 3 passes above the surface of the liquid developer thus regulating the size of the developer zone which contacts the latent image. The amount of developer to which the latent image is exposed has a bearing upon the density of the respective images and prints produced therefrom. The resulting developed image will then continue to rotate with the drum to transfer station 11 where it contacts transfer web 12 to which it is transferred upon pressure applied by the transfer roller 13. The web is fed and rewound by idler rollers 14 and 15, respectively. The image is fixed by heating unit 16. The surface of the rotating drum is then cleaned of its residual developer by brush 17 and is thus prepared for a new imaging cycle.

FIG. 2 represents an application of the process of the present invention utilizing a photoconductive drum as the imaging member. In FIG. 2 there is seen a photoconductivc drum generally designated 20 which consists of a conductive substrate 21 and a thin photoconductive layer 22 overlying the surface. The photoconductive cylinder rotates in the direction indicated by the arrow so as to pass charging device 23 which produces a uniform charge on the surface of the photoconductive layer. The charged surface then passes under exposure station 24 producing an electrostatic charge pattern 25 on the surface of the photoconductive layer 22. The latent image. continues around the drum until it reaches the development station which consists of a container 26 for the high resistance liquid developer 27. Immersed in the liquid developer is electrode 28, a substantial portion of which is covered with dielectric material 29. A high voltage source 30 connects the immersed electrode to ground. As the latent image passes above the surface of the immersed electrode, a potential is applied to voltage source 30 which causes the surface of the liquid developer to be deformed so as to selectively contact the electrostatic charge pattern on the surface of the image bearing member. This controlled development process permits the development of an image pattern having a specific density. The developed image then proceeds to transfer station generally designated 31 consisting of the transfer roller 32 and feed and take up rollers 33 and 34, respectively. The developed image is pressure transferred to the surface of a copy Web 35 and fixed, by any suitable means, such as a heat generating unit 36. The drum surface then passes the brush mechanism 37 which cleans the residual developer material from the surface of the photoconductive layer. The drum is then ready for recycling.

Although the immersed electrode of the present invention is represented in the illustrations as an electrode with a knife-like edge from which the charges are emitted, any suitable configuration may be employed which will achieve the desired effect. Thus, a series of needle-like electrodes may be employed to provide the necessary field and current density or a thin wire electrode may be used such as a corotron wire. In the latter instance it is generally desirable to utilize an insulated shield to partially enclose the corotron wire so as to direct the charge to the desired area of the liquid developer while preventing unnecessary loss of energy.

A Wide range of voltages may be employed in the present system. The applied potential will depend upon the desired image density, thus controlling the degree of image developer contact with the image-bearing support. The applied potential necessary to attain the desired effect will vary depending upon the spacing of the electrode with respect to the liquid developer surface, as well as the spacing of the surface of the liquid developer with respect to the image support member and the shape of the immersed electrode. Generally speaking, the emitting surface of the immersed electrode will be positioned about 1 to about 10 mm. below the surface of the liquid developer and the image support member -will be operated at a distance of about .5 to about 5 mm. from the surface of the liquid developer. When these distances are utilized the applied potential generally will range from about 5 kv. to about 10 kv.

Any suitable organic liquid having a high volume resistivity, preferably at least about 10 ohms-cm. or greater and a low dielectric constant preferably less than about 3.4, may be used in the course of the present invention. Typical liquids include aromatic hydrocarbons such as benzene, toluene, xylene, etc.; aliphatic hydrocarbons such as hexane, cyclohexane, heptane, etc.; halogenated hydrocarbons such as trichloroethylene or carbon tetrachloride; silicone oils and mixtures thereof. Any suitable colorant particle which may be suspended in the insulating liquid may be utilized. Typical particles are talcum powder, charcoal, aluminum bronze, sulfur, pulverized resins of all varieties such as ordinary rosin, sealing wax, coumarone-indene resin, the treated pine resins sold under the trademark Vinsol resin, and various other synthetic and natural resins. Hard waxes are also found suitable. Powdered dyes may also be used or the resin or other powder used may be dyed any color desired. For example, the Vinsol resin may be melted with a small proportion of nigrosene dye, cooled and pulverized to give a dark colored powder. The suspended colorant or toner particles are electrostatically charged and develop a latent image by migration to the image surface under infiuence of the image charge.

The specific image support member utilized will be determined by the particular process employed to form the electrostatic charge pattern. If the electrostatic charge pattern is to be formed at'a remote station and then transferred to the support member or formed directly on the support member by selective charge deposition, then generally any suitable insulating material may be used as the particular support. Typical dielectric materials include polyethylene, polyurethane, polyethylene terephthalate, polyvinyl chloride, polytetrafluoroethylene and polyvinyl fluoride. If conventional xerographic materials are used as the image bearing member, then a photoreceptor consisting of a base conductive support such as aluminum or steel will have coated on its surface a photoconductive layer in either a homogeneous form such as a selenium coating or in a suspension form of a photoconductive pigment in a carrier resin. Typical photoconductive compositions and plates are those as disclosed in U.S. Pat. No. 3,121,006; 3,121,007; and 3,151,982.

After development of the electrostatic latent image with the liquid developer the image may be then transferred to a secondary substrate or copy web by any suitable technique such as by pressure transfer or adhesive pickofl. Typical materials that may be used as a copy web support include polyethylene terephthalate, polyvinyl fluoride, polyurethane, polyethylene, and ordinary bond paper. Any suitable means may be used to fix the image formed on the copy web such as by placing a lamination over the top surface of the transferred pigment image or by heat or vapor fusing of the resulting image to the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To further define the specifics of the present invention the following examples are intended to illustrate and not limit the subject matter of the present invention. Parts and percentages are by weight unless otherwise indicated.

Example I 15 grams of a phenol modified pentaerythritol ester of rosin known under the tradename as Pentarol 20 is digested in 25 grams of xylene and when solution is completed, 15 grams of a linseed oil modified alkyd resin of medium oil length, known under the tradename Rhodene L6/100 is added. 150 grams of Phthalocyanine Blue is then added to the above mix and blended in a ball mill until mixing is complete and pigment particle size is reduced to about 0.5 micron, average. After about 8 hours of milling in the ball mill it is found that the pigment particles are coated with a thin film of the above mix. The resulting paste is dispersed in a chlorinated-fiuorinated hydrocarbon solvent, trichloromonofluoromethane, forming the developer liquid, approximately 0.5 gram of the mix being dispersed in 100 ml. of the liquid.

A coronode with a knife-like edge is immersed in the liquid developer which is contained in a trough-like arrangement. An electrostatic latent image formed on the surface of a zinc oxide plate is placed in a position about 2 mm. from the surface of the liquid developer. The immersed electrode has its discharge edge from which the corona is emitted situated about 5 mm. beneath the surface of the liquid developer opposite the imaged photoconductive plate. A voltage of about 7 kv. is applied to the immersed coronode. The surface of the liquid developer is selectively displaced by the applied voltage and contacts the surface of the imaged zinc oxide photoconductive substrate. Upon contact of the liquid developer with the imaged plate the coated pigment particles deposit on those areas of the image where a suitablpotential exists, until the charge of the image has been satisfied by the particles deposited, the particles being held in position by the electrical force until the carrier liquid present on the imaged substrate evaporates. A high density image is thus developed on the photoconductive plate.

Example II The following blend is prepared:

Grams Boiled linseed oil 25 Cadmium selenide (red) 75 Lead naphthenate 0.5

Example III The following developer paste is formulated:

Grams Pentarol 2O 15 Rhodene L6/ 15 Xylene 25 Phthalocyanine Blue 15 0 The Pentarol 20 is digested in xylene and when solution is complete the Rhodene L6/100 is added. The Phthalocyanine Blue is then mixed with the resins and blended in a ball mill until mixture is complete and pigment particle size is reduced to the required fineness of about 0.5 micron, average. The resulting blend is mixed in a ball mill for about 8 hours. About 0.5 g. of the developer paste is mixed in about 100 cos. of trichloroethylene. A Mylar substrate having an electrostatic latent image formed thereon is placed about 2 mm. above the surface of the liquid developer. A knife-like, longitudinally shaped coronode is immersed beneath the surface of the liquid developer opposite the latent image with the knife-like coronaemitting edge being about 5 mm. beneath the surface of the liquid developer. A voltage of about 7 =kv. is applied to the immersed electrode which deforms the liquid developer such as to contact the latent image on the Mylar sheet. Following development of the latent image the excess solvent evaporates from the surface of the Mylar substrate, thus leaving a high density image developed on the surface of the Mylar substrate.

Example IV The process of Example I is repeated with the exception that the coronode is located about 1 mm. beneath the surface of the developer solution. The developer solution is thus presented to the latent image in the form of a spray which develops the image in a manner similar to that disclosed in Example I. A high density image is produced.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples With similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used, if desirable. For example, multiple development stations may be used in the development process. In addition, other materials may be incorporated in the imaging suspension, the immersed coronode, or the particular image support to enhance, synergize, or otherwise desirably affect the properties of the process of the present invention. For example, the developer liquid may contain thickening agents so as to effectively control the viscosity of the developer solution.

Anyone skilled in the art will have other modifications occur to him based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A process of image development comprising forming an electrostatic latent image on the surface of an image support member, positioning said image bearing member in close proximity to the surface of a liquid developer suspension, said suspension comprising developer particles dispersed in an insulating carrier liquid, said developer having immersed beneath the surface at least one coronode 8 capable of emitting charge to the surrounding liquid References Cited environment, and applying a potential to said immersed UNITED STATES PATENTS coronode of such a magnitude to selectivity deform the surface of said liquid developer in a controlled manner so 3,084,043 4/ 1963 Gundlach 96 1 as to contact the latent image on said support member, thereby developing said image. 5 GEORGE F. LESM-ES, Primary Examiner 2. The process as disclosed in claim 1 wherein said image support member comprises an insulating substrate having a latent image electrostatically formed thereon. U S C1 X 3. The process as disclosed in claim 2 wherein said insulating substrate is a photoreceptor. 118637; 1l737LX; 252-62.1

M. B. WITTENBERG, Assistant Examiner 

